Breast cancer is the most common cancer among women in America, accounting for 15 percent of all cancer deaths. Survival depends strongly on early diagnosis. The foremost breast cancer screening tool is the x-ray mammography. It is estimated that, each year, over 34 million mammograms are conducted in the United States. X-ray mammography can be used to detect variations in tissue density, and when an abnormality is detected, further tests are employed to detect the exact cause of the anomaly.
X-ray mammography is often insufficient for the early detection of breast cancer. Consistent quality is technically difficult to produce and interpretations are variable and subjective. Dense breast tissue and breast cancer both appear white on a mammogram. Therefore, although conventional screening methods have been proven to reduce mortality in women above age fifty, the efficacy of mammography as a life-saving measure in young women is uncertain.
Especially problematic among young women is the higher rate of false-positive and false-negative results. False positives result in over-diagnosis and over-treatment (e.g., 75 percent of biopsied lesions resulting from suspicious mammogram findings turn out to be benign). Furthermore, the false-negative rate has been determined to be as high as 34 percent, increasing the potential mortality for one third of the screened population.
The conventional mammogram is a series of two x-rays, one in the mediolateral oblique view (i.e., from side) and one in the craniocaudal view (i.e., from above). Each film requires uncomfortable compression of the mammary tissue. The mammogram does not detect cancer directly, but is a measurement of tissue abnormalities. Microcalcifications, architectural distortions, masses, and asymmetrical densities can be imaged using this modality. However, conventional mammography cannot distinguish between tissue types or distinguish between in situ lesions or invasive cancer.
Breast biopsies are currently a vital part of the breast cancer screening and detection process to determine the type of tumor harbored in the breast. Biopsies are also able to identify whether the tissue examined is healthy. When the biopsy proves that the anomalous tissue detected by x-ray mammography is indeed healthy, the mammography is said to have produced a false positive. Studies show that testing costs for false positives may be near one-third of the entire mammography cost per year. It has been stated that nearly 75 percent of all tissue biopsies are deemed benign. While the monetary cost is one consideration, the emotional burden ensuing from false-positive results provided by the mammogram cannot be neglected. Women who experience false positives suffer from impaired emotional states for up to three months, with symptoms including impaired moods and limited daily functions. In addition, fear of breast cancer is instilled in most patients receiving false-positive results.
On the other hand, the fact that x-ray mammography machines have sensitivity ratings between 83 and 95 percent leaves them open to missing cancerous growths in the breast tissue. In addition, radiologists' interpretations are not 100 percent accurate and can miss lesions that appear on the film. Poor film quality caused by inadequate x-ray mammographic techniques can also lead to false negatives. Delay in treatment and uncontrolled progression of the disease are possible outcomes of false negatives. In fact, the leading cause of action in medical malpractice lawsuits arises from late or missed breast cancer diagnoses.
Electro-impedance tomography (EIT) is a safe and effective tool for imaging breast tissue regardless of density. The electrical properties of tissue have interested scientists for over 200 years, and researchers have been studying the electrical properties of breast tumors from as early as 1926. The consensus is that malignant breast tumors differ from normal healthy tissue with respect to their electrical properties. Differences in cellular water and electrolyte content, cell membrane permeability, and cell packing reduce the impedance of cancerous tissue. Research in the use of EIT for mammography has resulted in the successful diagnosis of breast cancer in women. Unlike x-ray mammograms, which require a biopsy to differentiate between suspicious tissue types, EIT technology is capable of differentiating among tissue types with less need for biopsies. Furthermore, EIT mammography can create three-dimensional images, which is beyond the capabilities of x-ray mammography. Overall, impedance tomography is more effective, more efficient, and more convenient than x-ray mammography.
EIT mammography is also more economical than x-ray mammography. Impedance-measuring equipment is both compact and inexpensive. The equipment uses small amounts of electricity to run, costing less per image generated. The images are generated on a computer screen and the clinician may print the important images during the examination. Expensive films are unnecessary since tissue images can be printed on less-expensive, high-quality paper or stored and analyzed in pure digital format. In addition, impedance mammography can identify tissue types, reducing the need for biopsy of suspect tissue regions. These factors culminate in a product that is inexpensive to manufacture, inexpensive to operate, and cost-effective.
There are several challenges to creating an effective EIT system. Many current two-dimensional systems create an image of impedance parameters in a single coronal plane (e.g., a view from the front). However, two-dimensional imaging is insufficient to yield clinically accurate results. For example, during impedance scanning of a three-dimensional cylinder, current will naturally traverse out of the two-dimensional imaging plane, extending approximately half of the radius above and below the plane. The presence of heterogeneous tissue above or below the imaging plane will affect the reconstructed images. Three-dimensional EIT is necessary to achieve an accurate reconstruction of the results.
Several research teams have made effective and efficient three-dimensional EIT systems. One obstacle to be overcome is the integration of a three-dimensional electrode array with imaging software. Geometry and size of the tissue to be imaged are two important parameters that must be considered for creation of an accurate image. Both parameters are variable among women. A static geometric electrode array is necessary for comparative studies and clinical use.
Previous applications of EIT have relied heavily on the quality of the contacts between the electrodes and the skin. Errors in placing the electrodes, which cannot be avoided even when the electrodes are applied by a skilled technician, can lead to errors in determining the size and location of anomalous tissues. Further, the electrical signals detected at the electrodes can be distorted by reflective and refractive noise at the skin surface that electrode placement gels neglect. Imaging based on data from electrodes contacting the skin requires the development of a software model that approximates the variations in size and shape of the tissue structure being imaged. For example, if an inflated rubber glove were used as the image of a hand, no person's hand could be accurately imaged. Furthermore, the degree of inaccuracy would vary by patient, making variations difficult to correct by means of software. Instead of fitting breast tissue to a static array or adjusting software for each patient, the technology disclosed herein presents an alternate approach to EIT imaging.